1. Field of the Invention
The present invention relates to a cable-type steering device in which a steering wheel and a steering gear box are connected to each other by easily-flexible operating cables such as Bowden cables.
2. Discussion of Background Art
A conventional cable-type steering device is known, for example, from Japanese Patent Application Laid-open Nos. 2000-25623, 10-59197 and 8-2431.
In these cable-type steering devices, a driving pulley, a follower pulley and pulley shafts are generally constituted by separate members, and a pulley boss and the pulley are relatively non-rotatably coupled to each other at a serration-coupling portion or a spline-coupling portion.
However, a slight play or looseness provided in the serration-coupling portion or the spline-coupling portion in order to absorb a misalignment between the pulley and the pulley shaft, brings about the following problems: the pulley is vibrated relative to the pulley shaft due to the vibration transmitted from wheels which causes a noise, and a steering feeling is deteriorated during operation of the steering wheel.
The present invention has been accomplished with such circumstance in view, and it is an object of the present invention to eliminate the play or looseness between the pulley and the pulley shaft in the cable-type steering device, to prevent noise and deterioration in steering feeling.
To achieve the above object, according to a first aspect of the present invention, there is provided a cable-type steering device in which a driving pulley coupled to a first pulley shaft connected to a steering wheel and a follower pulley coupled to a second pulley shaft connected to a steering gear box are connected to each other by operating cables, whereby a steering torque input to the steering wheel is transmitted through the operating cables to the steering gear box, wherein at least one of transmission of a steering torque between the driving pulley and the first pulley shaft and transmission of a steering torque between the follower pulley and the second pulley shaft is carried out through a tapered coupling portion of a tapered surface formed on an outer periphery of at least one of the first and second pulley shafts and a tapered surface formed on an inner periphery of at least one of the driving pulley and the follower pulley.
With the above arrangement, the transmission of the steering torque between the driving pulley and the pulley shaft of the driving pulley or the transmission of the steering torque between the follower pulley and the pulley shaft of the follower pulley is carried out through the tapered coupling portion of the tapered surface of the pulley shaft and the tapered surface of the pulley. Therefore, it is possible to eliminate the play provided when such transmission is carried out through the serration-coupling portion or the spline-coupling portion, thereby bringing the pulley shaft and the pulley into close contact with each other without a gap. Thus, in contrast to conventional cable-type steering devices it is possible to prevent a noise from being generated from the driving pulley or the follower pulley due to the vibration of a vehicle body, and to prevent a play in the steering wheel from increasing to deteriorate the steering feeling.
According to a second aspect of the present invention, in addition to the arrangement of the first aspect, the pulley having the tapered surface is axially movably supported in a casing so that such pulley is axially biased by a nut screwed over the pulley shaft having the tapered surface, thereby coupling the pulley shaft having the tapered surface and the pulley having the tapered surface in close contact with each other at the tapered coupling portion.
With the above arrangement, each of the pulleys having a tapered surface can be axially biased by a load of the nut screwed over the corresponding pulley shaft having a tapered surface without an excessive load acting on the pulley casing, to strongly couple the pulley shaft and the pulley in close contact with each other at the tapered coupling-portion, so that they do not slip relative to each other.
A driving pulley casing 12 and a follower pulley casing 14 in an embodiment correspond to the pulley casings of the present invention.